This invention relates to semiconductor logic devices which can be integrated in high density and more particularly to a semiconductor logic device suitable for electrically rewriting the logic design or structure.
In the past, a logic LSI comprised of standard cells or gate arrays has been known. Programmable logic devices comprised of electrically rewritable or programmable elements are described in, for example, U.S. Pat. No. 4,124,899 (issued to Birkner et al on Nov. 7, 1978), U.S. Pat. No. 4,609,986 (issued to Hartmann et al on Sept. 2, 1986), U.S. Pat. No. 4,642,487 (issued to Carter on Feb. 10, 1987) and JP-A-61-280120. A relevant description is also given in ISSCC (International Solid-state Circuits Conference) 86 (1986), pp. 244-245.
In the prior art logic LSI, layout of cells and wiring in the standard cells or gate arrays are changed by changing the mask pattern in the course of fabrication of the LSI to obtain a desired logic design. This raises a problem that it takes a long time to materialize an LSI having necessary functions.
On the other hand, the prior art programmable logic device using electrically programmable elements is insufficient to realize a large-scale and high-integration-density logic design. For example, in the aforementioned U.S. Pat No. 4,124,899, the wiring between mutually relatively distant logic cells and the structure of multi-stage logic are not considered which become problematic as the scale of logic increases. According to a description given on pp. 244-245 and 359-360, 1986 IEEE ISSCC, a feedback path is used for constructing a multi-stage logic, but the array has a structure in which all word lines intersect with all output lines.
The aforementioned U.S. Pat. No. 4,609,986 uses a hierarchical array structure having a global feedback path and a local feedback path but logic between discrete logic cells is of the global feedback path and constructed on a common array.
On the contrary, in the aforementioned U.S. Pat. No. 4,642,487 and JP-A-61-280120 laid open on Dec. 10, 1986, logic cells are interconnected together by a dedicated wiring having a bus switch.